Somewhere out there are 200,000 stars that are about to get their picture taken. Much more important, there are who-knows-how-many planets circling those stars, and there’s at least a chance that there will be organisms on some of them that could smile for the camera. That’s the hope, at least. And NASA’s Transiting Exoplanet Survey Satellite (TESS), is about to try to make it a reality. The launch of the spacecraft, originally set for April 16, but scrubbed due to a guidance problem in its SpaceX Falcon 9 rocket, is now set for Wednesday, April 18.
Planet-hunting is a relatively new field for astronomers. Until very recently, we knew of no other stars in the universe other than our own sun that are circled by planets. It was in 1992 that the first two exoplanets were discovered orbiting a pulsar—a rapidly rotating neutron star—2,300 light years from Earth. In 1995, the first exoplanet orbiting a sun-like star was discovered. But it was not until the Kepler Space Telescope was launched in 2009 that the exoplanet population exploded. In the nine years that the now-aging Kepler has been aloft, it has detected 2,343 confirmed exoplanets, as well as another 2,244 candidate planets that need further study.
Kepler was designed to do its work in the most boring way possible: by staring unblinking at a single ten-degree by ten-degree square in the 360-degree bowl of the sky, looking for the tiny dimming of light that occurs when an orbiting planet passes in front of its star. That single observation can reveal both the diameter of the planet and its orbital period, or how fast it makes a single revolution. That, in turn, can tell you something about whether it’s Earth-like, and thus potentially habitable.
The problem is that Kepler’s narrow but deep look into the cosmos turned up a lot of extremely far-off exoplanets thousands of light years away. That kind of distance limits how much can be learned about them with even the best telescopes. TESS’s mission is different. During the two years of its planned operation, it will survey the entire sky—not just a mere postage stamp-sized portion of it—and it will be selective in the stars it studies. The spacecraft’s four on-board cameras will focus on the 200,000 nearest and brightest stars in its field of vision, as they best lend themselves to follow-up studies. In addition, some of TESS’s work assignments will be crowdsourced — astronomers will be allowed to request observations of 20,000 additional stars that may not make TESS’s own cut but that the scientists believe hold exoplanet promise.
TESS will not remotely seal the deal on whether any exoplanets it discovers are capable of harboring Earth-like life, much less if they actually do harbor such life. Other telescopes on the ground will have to make further observations, principally using what’s known as the radial velocity method, which measures the degree of gravitational wobble a planet causes in its star. That yields information about a planet’s density and composition, as opposed to its diameter. Observations with future satellites will also analyze the light of a star as it streams through a planet’s atmosphere—assuming the planet has an atmosphere at all—looking for the chemical fingerprints of biological activity, including methane, carbon dioxide and oxygen.
For now at least, reasonable scientific minds will continue to differ on whether life exists anywhere in the universe beyond our one Earthly terrarium. But no one differs any longer on the fact that there is a multitude of worlds on which life at least could take hold—and TESS is about to find even more.